The disclosure relates to a control valve for adjusting a process medium flow of a technical process installation, like a refinery, a food processing plant like a brewery, or a petrochemical plant or the like.
Technical process installations are meant to work automatically to a large extent, which is why process parameters of the process medium flow, like the position of the control valve, are very important control variables. These parameters are commonly communicated to a central control unit or to a positioner controlling the control valve. However, for many of the employed control valves an electrical infrastructure for generating, transmitting and/or processing information signals is not readily provided. It is known, for example, to employ a wireless communication. In locations where accessibility is enabled for a simple fitting of signal lines or where a high safety standard for signal transmission is required, the classical signal transmission via wires is to be preferred.
Principally, for all processes of signal generation and transmission there is the problem to provide a power supply that is battery-less and ignition-proof as far as possible. In particular for pneumatically driven control valves there are endeavours to fit, for example, small turbines into the pneumatic operating actuators, thus converting the pneumatic energy into electric power. However, for such air-powered mini turbines the principle problem exists that in case of failing air pressure supply a continuous power supply is not possible without use of a battery. The usage of mini turbines within the process medium flow is also not uncritical in so far as critical conditions prevail within the process fluid, in particular if the process fluid contains particles. Furthermore, hardly any long-term studies exist about these types of systems which provide for a reliable supply of power.
A continuous power supply by means of an energy converter for electro-pneumatically operated positioners for use in technical process installations is known from DE 10 2006 011 503 A1. By means of a piezoelectric element, a thermoelectric element or a mechanical turbine, electrical power is to be provided out of the air pressure supply by utilizing a pressure difference between ambient air and a pressure of the air supply for actuating a control valve.
In this technology the self-sufficient continuous power supply achieved depends on the continuous presence of pressurized air as an energy supply. However, in technical processing installations it frequently occurs that the air pressure supply fails, so that an electrical power supply, for example for determining the control valve position, cannot be provided continuously. Furthermore it appears that changes in air pressure often also necessitate a complicated electrical control procedure for the power supply. Besides, control devices can also be actuated by electromotive drives.